Flash lamp



April 13, 1943. E. LEMMERS FLASH LAMP Filed Jan. 21, 1942 m e uJ 3 a 8 m m m nL w. we .B U H. 4 G E Q .F. .UJ b m 5 w E F w 3. Q F. m H m l Patented Apr. 13,1943

FLASH LAMP Eugene Lemmers, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application January 21, 1942, Serial No. 427,598

7 Claims.

My invention relates in general to photoflash lamps and similar devices comprising a sealed envelope, and more particularly to the provision therein of means for facilitating testing of such devices for the presence of air or other foreign gases by formation of a high frequency glow discharge in the envelope. The inventionis especially useful in testing photoflash lamps of the type disclosed in copending application Serial No. 328,399--Marvin Pipkin, filed April 8, 1940, in which the source of actinic radiation is constituted by one or more beads or compact masses of an agglutinated flashlight powder or fulminating material disposed within a sealed glass bulb.

As a safeguard against explosion of the glass bulb when flash lamps are flashed, it is common practice, in the manufacture of such flash lamps, to test th completed lamp for the presence 'of air in the sealed bulb. One well-known method of conducting such a test, known as a coil or glow test, consists in the use of high frequency equipment to produce a glow discharge in the sealed bulb. By observing the color of the glow discharge within the sealed bulb, the presence or absence of air therein can then be readily determined, a pale bluish-green glow discharge'denoting a good lamp containing the normal oxygen gas filling with no air present and a purple or pink-colored glow discharge indicating a, lamp into which air has leaked.

To prevent the ignition of the fulminating material in flash lamps of the above described type by the high frequency glow discharge, and therefore the premature flashing of the lamp, it has been found necessary to confine the glow discharge to an area within the bulb remote from the fulminating material therein.

One method of accomplishing this result is by the passage of the high frequency discharge between two spaced points on the bulb surface remote from the fulminating material, as described and claimed in my copending application Serial No. 427,597 filed of even date herewith. Although such method is eminently satisfactory, under certain conditions the breakdown of the gaseous atmosphere within the bulb and the resulting formation of the glow discharge therein occurs only after a relatively prolonged period of time follow- One object of my invention is to provide a sealed container of insulating material having means therein for facilitating the development of a high frequency glow discharge therein between two points on the container wall.

Another object of my invention is to provide a flash lamp having means for facilitating the development of a high frequency glow discharge within the sealed bulb between two points of the bulb wall.

A feature of the invention is the provision of an electrically conductive member or electrode on the inner surface of the sealed container and extending part of the distance between the two points on the container surface between which the high frequency discharge is to pass to thereby shorten the discharge gap within the sealed container and so facilitatethe initiation of the discharge therein. I

Further objects and advantages of my invention will appear from the following description of species thereof and from the accompanying drawing in which:

Fig. 1 is a perspective view of a flash lamp comprising my invention; Fig. 2 is an elevation, partly in section, of the flash lamp shown in Fig. 1; Figs. 3 and 4 are fragmentary perspective views of two modified forms of flash lamp comprising my invention; and Fig. 5 is a diagrammatic illustration of an arrangement for testing flash lamps comprising the invention for the presence of air therein.

Referring to the drawing, the flash lamp there shown comprises a bulb ID of a suitable'lighttransmitting material such as glass and having a bulbous or active portion II and a neck l2: The

'' bulb I0 is sealed and filled with a combustion suping the application of the high frequency current porting gaseous filling, preferably oxygen, at a suitable pressure, for instance, from mm. of mercury up to one atmosphere or so. To minimize cracking of the bulb on charge flashing and to render the bulb substantially shatterproo'f, a suitable light-transmitting varnish or lacquer is coated on the inner or outer surface, or both surfaces, of the bulb. Sealed into the bulb in and extending thereinto from the neck portion thereof is a mount structure comprising a reentrant stem 13 having a pair of leading-in wires l4, l4 sealed into the press portion l5 of the stem and extending therethrough to the terminals of a base l6 secured in a suitable manner to the neck of the bulb. The leading-in wires 14, I4 are provided with juxtapositioned parallel inner lead portions I1, I! preferably terminating at a point centrally of the active portion l I of the bulb Ill.

Mounted substantially centrally within the bulb i is a small'ignition filament ll interconnecting the inner leads II at their inner extremities and consisting of a straight length of wire of a suitable refractory material, preferably tungsten.

- Disposed partly on the filament I8 and partly on the adjacent portions of the Juxtapositioned inner leads i1, i1 is a layer or coating of a suitable fulminating light-giving substance l8 such as disclosed in copending applications Serial Nos. 828,399 and 424,166, Marvin Pipkln, filed April 8, i940, and December 23, 1941, respectively. The said substance ii constitutes the sole source of actinic light produced by, the light, and because of its disposition adjacent the filament i8, is therefore located in the bulb at a point remote from the top thereof. The light-giving substance is preferably consists of a mixture of zirconium metal powder, potassium perchlorate powder and sodium chlorate powder bonded together by a suitable binder such as nitrocellulose.

In accordance with the invention, a suitable electrically conductive member or electrode is provided in the lamp bulb closely adjacent the inner surface of the bulb wall and extending part of the way only between the two spaced points on the bulb between which the high frequency discharge is to pass during the glow testing of the lamp. The conductor 20 serves to shorten the discharge gap within the lamp bulb and therefore facilitates the starting of the high frequency glow discharge therein. As a consequence, the glow discharge is initiated in the lamp bulb in a relatively short period of time, i. c., in a fraction of a second, under practically all bulb gaseous filling conditions, even where the bulb is completely filled with-air.

The conductor 20 is preferably located adjacent the top or upper portion of the bulb surface, as shown in the drawing, since the high frequency glow discharge produced in the lamp bulb during tile testing thereof is preferably formed in the upper portion of the bulb. The conductor 20 may be of any suitable form and shape which wiil accomplish the intended object of shortening the discharge gap within the bulb. Preferably, however, the conductor or electrode 2|] comprises a conductive strip or wire or a conductive coating attached to or supported on the inner surface of the bulb wall. Thus, the conductor may consist of a thin band or layer 20 of determinate length of a suitable conductive material, such as aluminum or bronze paint or carbon, coated or painted on the inner surface of the bulb wall; or it may consist of a short determinate length of wire or strip material secured or attached in'any suitable manner to the inner bulb surface as by a lacquer or similar adhesive substance.

As shown in Fig. l, the conductor 20 may be in the shape of a single straight length of wire, strip or conductive coating extending a short distance in opposite directions from the top of the bulo. While such a construction adequately serves the purpose of shortening the discharge gap in the bulb, it may be desirable to employ two or more such straight conductive wires or strips arranged at an angle to one another in the shape of a cross or in cries-cross form as shown in Fig. 3.

In the modification shown in Fig. 4, the conductor or electrode is conveniently constituted by a trade mark or other insignia 2i imprinted on the inner surface ofthe bulb and consisting of a coating of conductive material such as a metal powder or paint, as described above.

Fig. 5 illustrates one arrangement for testing flash lamps comprising my invention for the leakage of air thereinto by the formation of a high frequency glow discharge therein. As shown, the apparatus comprises a glass cup or receptacle 22 having a seat 23 in its bottom wall against which the top of the lamp bulb to be tested is adapted to rest. The seat 23 is provided with a recess 24 which is filled with a very heavy electrically conductive liquid 25, such as mercury. The mercury filling 25 forms one of the high frequency discharge electrodes of the device and is connected by leading-in wire 28, which is sealed through the bottom wall of the glass cup 22, to one end of the secondary 28 of a Tesla coil 21 the other end of which is grounded. Filling the glass cup 22 up to a level high enough to just cover the mercury 25, for instance, to a depth of about to 3/ or so, is a suitable liquid insulating medium 28. Disposed on top of the liquid insulating medium 28, in the form of a supernatent, is an electrically conductive liquid 20 which forms the other high frequency discharge electrode of the device, the supernatant 30 being connected to ground by lead II. The two liquids 20,, Ill should be immiscible in one another, and in addition, the electrically conductive liquid 30 should be of appreciably lower specific gravity than that of the liquid insulating medium 29 so that it will always float on top the latter. The electrically conductive supernatent 20 may conveniently consist of water, in which case the liquid insulating medium 29 preferably consists of either trichiorethyiene or carbon tetrachloride. The primary 82 of the Tesla coil 21 is connected to a suitable source I! of high frequency current.

The flash lamp to be tested is inserted in the glass cup 22 and properly positioned therein so that the tip of the bulb l0 engages in the seat 28 and contacts the mercury 28 therein. In such position, the tip of the bulb will be submerged in the two liquids 28, I0, and the internal electrode or conductor 20 will lie opposite the mercury 25 but will be spaced a slight distance from the nearest point on the inner surface of the bulb wall opposite the electrically conductive liquid 30. The source of high frequency 32 is then energized, with the result that a small glow dischargeforms within the bulb iii between the internal electrode or conductor 20 and the nearest points on the inner surface of the bulb wall opposite the external liquid electrode It], as indicated'at 84. The glow discharge 34 is thus confined to a small area within the top portion of the bulb so as to be remote from the fulminating material l8 therein, and therefore will not ignite the fulminating material l9 and so prematurely flash the lamp. Because the internal electrode or conductor 20 shortens the discharge gap within the bulb til, it therefore materially facilitates the initiation of the glow discharge in the bulb. By observing the color of the glow discharge, the presence or absence of air in the bulb can then be readily determined, as described hereinbefore.

What I claim as new and desire to secure by Letters Patent of the United States is:

i. In a flash lamp comprising a sealed bulb at least a substantial portion of which is free of metallic conductor material, said bulb containing a gaseous filling and a quantity of fulminating material, means for facilitating the initiation of a high frequency discharge within the bulb at a point remote from said fulminating material and between two spaced points on the wall of said bulb portion, said means comprising a conductive electrode member disposed within said bulb and arranged to shorten the discharge gap between the said spaced points of the bulb wall.

2. In a flash lamp comprising a sealed bulb at least a substantial portion of which is free of metallic conductor material, said bulb containing a gaseous filling and a quantity of fulminating material, means for facilitating the initiation of a high frequency discharge within the bulb at a point remote from said fulminating material and between two spaced points on the wall of the said bulb portion, said means comprising a'metallic conductor extending between but terminating short of at least one of the said spaced points of the bulb wall to thereby shorten the discharge gap within said bulb. I

3. A flash lamp comprising a sealed bulb at least a substantial portion of which is free of metallic conductor material, a gaseous filling in -said bulb, a quantity of f-ulminating material disposed within said bulb, and conductive means for facilitating the initiation of a high frequency discharge within the bulb at a point remote from said fulminating material and between two spaced points on the wall of said bulb portion, said means being disposed within said bulb and extending a relatively short distance closely alongside a portion of the wall of the said bulb portion at a point remote from said fulminating material.

4'. A flash lamp comprising a sealed bulb containing a gaseous filling, a quantity of fulminat-T ing material disposed within said bulb at a point remote from the top portion of the bulb wall, said fulminating material constituting substantially the sole source of actinic radiation of the lamp, and conductive means for facilitating the initiation of a high frequency discharge within the bulb at a point remote from said fulminating material and between two spaced points on the wall of said bulb portion, said means being disposed within said bulb closely adjacent and extending a relatively short distance alongside the said top portion of the bulb wall.

5. A flash lamp comprising a. sealed bulb containing a gaseous filling, a quantity of fulminating material disposed within said bulb at a point remote from a given portion of the bulb wall, said fulminating material constituting substantially the sole source of actinic radiation of the lamp, and means for facilitating the initiation of a high frequency discharge within the bulb at a point remote from said fulminating material and between two spaced points on the wall of said bulb portion, said means comprising a conductor secured to the inner surface of the said portion of the bulb wall and extending a relatively short distance therealong.

6. A flash lamp comprising a sealed bulb containing a gaseous filling, a quantity of fulminating material disposed within said bulb at a point remote from a given portion of the bulb wall, said fulminating material constituting substantially the sole source of actinic radiation of the lamps, and means for facilitating the initiation of a high frequency discharge within the bulb at a point remote from said fulminating material and between two spaced/points on the wall of said bulb portion, said means comprising a relatively short stripe of conductive material on the inner surface of the said portion of the bulb wall.

7. A flash lamp comprising a sealed bulb containing a gaseous filling, a quantity of fulminating material disposed Within said bulb at a point remote from a given portion of the bulb wall, said fulminating material constituting substantially the sole source of actinic radiation of the lamp, and means for facilitating the initiation of a high frequency discharge within the bulb at a point remote from said fulminating material and between two spaced points on the wall of said bulb portion, said means comprising a coating of conductive material in the form of an insignia on the inner surface of the said portion of the bulb wall.

' EUGENE LEMMERS. 

